High alumina refractories

ABSTRACT

Disclosed herein is a refractory brick batch mix which consists essentially of, by weight, about 85 to 96 percent alumina, about 3.99 to 13.99 percent silica, about 0.01 to 0.5 percent of a lithium compound capable of oxidizing to lithium oxide, and about 1 to 5 percent bentonite. Refractories prepared from these mixtures exhibit increased strength, higher density, lower porosity and higher refractoriness compared to those previously available.

United States Patent Bakker 1 Feb. 8, 1972 [541 HIGH ALUMINA REFRACTORIES [72] lnventor: Wate T. Bakker, Severna Park, Md.

[73] Assignee: General Refractories Company, Philadelphia, Pa.

[22} Filed: May 29, 1969 211 Appl. No: 829,132

52] us. Cl ..l06/65, 106/67 Field of Search ...106/65, 67

[56] References Cited UNITED STATES PATENTS 2,559,343 7/1951 Caton ..l06/65 3,067,050 12/1962 Miller 106/65 3,230,102 1/1966 Miller 106/65 3,303,034 2/1967 Troell et a1. 106/65 Primary Examiner-James E. Poer Attorney-Everett H. Murray, Jr. and Francis D. Neruda ABSTRACT 8 Claims, No Drawings HIGH ALUMlNA REFRACTORIES This invention relates to refractories of high-alumina content by which is meant, for the purposes of this invention,

refractories containing at least about 50 percent by weight of A1 0,.

High-alumina refractories are generally classified by their A1 content in groups having, approximately, 50, 60, 70, 80, 90, or 99 percent A1 0 by analysis. Those containing 50 to 90 percent A1 0 are prepared by blending various high-alumina refractory materials, while those containing as much as 99 percent A1 0 are essentially high-purity alumina. The most common high-alumina refractory materials and their typical Al O contents are fused alumina, 99.5 percent; sintered alumina, 99.5 percent; calcined alumina, 99 percent; fused bauxite, 95 percent; calcined South American bauxite, 88'percerlt; calcined Alabama bauxite, 74 percent; calcined diaspore, 76 percent; burley diaspore, 48and 58 percent; and kyanite, 56 percent. All of these materials are chemically compatible, and

so they can be blended to provide almost any desired resultant alumina content.

The present invention is concerned with thosehigh-purity high-alumina refractories containing by weight in the range of about 85 to 95 percent alumina. In addition to the alumina, these refractories generally contain in the range of'about 5 to percent silica with minor amounts of impurities such as TiO Fe 0 alkalies and alkaline earths normally associated with the alumina and silica ores.

Ordinarily, high-alumina refractory bricks or shapes are manufactured from relatively pure, high-density A1 0 grog material and a siliceous binder. Traditional forms of silica used for this purpose are various kinds of clays, usually kaolin or ball clay, and ground silica sand. The use of clay, at least in large amounts, is objectionable because during firing the clay decomposes into mullite and a glassy phase, the glassy phase forming the bond between the grog grain, which structure decreases the refractoriness of the brick under load. The use of ground silica, on the other hand, increases the refractoriness under load of the brick, probably because the silica reacts with the alumina in the solid state to form mullite so that little or no glass is formed. However, because of the low reactivity of the silica, this reaction is slow and only very little mullite is formed at conventional burning temperatures. Therefore, these refractories have a low-cold strength and most of the mullite in the brick is formed during service-leading to an undesirable large reheat expansion.

It was discovered that high-alumina refractories possessing high-cold strength and low-reheat expansion could be prepared by incorporating in the batch mix about 0.05 to 0.2 percent of lithium fluoride or lithium carbonate and about 0.01 to 0.3 percent of at least one compound selected from the group consisting of calcium hydroxide, .magnesium hydroxide and iron oxide. Such refractories. are described in US. Ser. No. 741 ,333 which was filed on July 1, 1968 and is in the hands of a common assignee and incorporatedherein by reference thereto. While refractories prepared in this manner exhibit characteristics superior to those of the prior'art, they lack sufficient high-pressed density and low porosity.- Accordingly, the discovery of a means whereby these shortcomings could be overcome simply and economically would constitute a significant and important advance in the art. The present invention providesjust such a means.

It is among the objects of this invention to provide high alumina refractories which, as compared with those previously available, are of increased strength, higher density, lower porosity, and higher refractoriness, and which may be produced from readily available high aiumina materials by practices which are customary in the refractory trade.

Another object is to provide a brick batch mix suitable for producing refractories in accordance with the foregoing ob ject.

A further object is to provide a simple and economical method of making refractories in accordance with the firstnamed object.

Still other objects and advantages will-become apparent from a consideration of the following specification and claims.

represent-invention is predicated upon the discovery that the incorporation of a small amount of a lithium compound to a-highvalumina refractory batch mix, as hereinafter discussed in-detail, plus a smalltamount of bentonite, as also discussed hereinafter, increases the pressed density. of the resulting burned brick while at the sametime decreasing its apparent porosity without deleteriously. affecting its refractoriness under load. In fact, improvement in the refractoriness under load has been realized through the stated additions.

More specifically,.the presentinvention involves a high-purity'aluminarefractory brick batch mix consisting essentially of, by weight, about 85 to 95 percent alumina; about 3.99 to 13.99 percent silica; about 0.01 to 0.5 percent of at least one lithium compound;. and about 1 to 5 percent of bentonite. Preferably, the refractory brick batch mix will consist essentially'of, by weight, about 88 to .92 percent alumina; about 5.95 to 9.95 percent silica; about 0.05 to 0.2 percent lithium compoundiand about 2 to 3 percent bentonite. The percentages employed' herein are based on the total weight of the refractory mix.

Asnoted hereinbefore, alumina is available in varying grades and purities. Generally the alumina employed in this invention will be a high purity grade, that is, it will contain at least about 99 percent A1 0 preferably at least about 99.5 percent A1 0 The alumina grog maycomprise alumina which is sintered, tabular, fused, calcined or the like. However, as is common in high-alumina refractory brick manufacture, a significant portion of the alumina will ordinarily constitute relatively coarse particles, and the remaining portion will be made up of relatively fine particles. Thus, for example, from about 50 to about 65 percent, by weight, of the alumina will be in the range of 6 to +48 mesh (Tyler) and the balance (from about 35 to about 50 percent, by weight) will be -48 to -400 mesh. Preferably, at least about 10 to 30 percent by weight, of the alumina will be -325 mesh or finer.

Similarly, the silica component will also be a high-purity material, that is, containing at least about 99 percent SiO preferably over-99.5 percent SD: and especially about 99.9 percent SiOg. In this respect, ground glass sand is particularly suitable. Generally, silica will be substantially 200 mesh, and preferably at least about 50 percent, by weight, thereof will be -325- mesh or finer.

In addition to the alumina and silica, the refractory brick batch mix will have incorporated therein bentonite and a lithium compound; The lithium compound employed should be capable of forming, that is, oxidizing to-lithium oxide during the firing ofthe pressed brick batch mix when said lithium compound is-present therein. Lithium carbonate and lithium fluoride are particularly suitable in this respect. Lithium fluoride is especially preferred. However, the lithium carbonate is quite desirable because of its relative cheapness and ease of handling. Whichever lithium compound is employed, such should be relatively finely divided, that is, substantially all thereof should be 100 mesh, and preferably 325 mesh. As previously indicated, the amount of lithium compound incorporated in the mix should constitute about 0.01 to 0.5 percent thereof. Higher amounts markedly decrease the refractoriness under load of the resulting brick.

The other essential component incorporated in the mix according to the present invention is-the-mineral bentonite. As with most naturally occurring substances, the composition of bentonite will varytosome degree. The chemical analysis of a typical bentonite utilizable in accordance with this invention would be as follows:

This material is comparatively inexpensive and readily available. Generally, as is the case with the lithium compounds, the bentonite should be relatively fine. Specifically, the major portion thereof should be l mesh, and preferably 325 mesh.

these examples which readily suggest themselves to those skilled in the art without departing from the spirit of the present invention and/or the scope of the appended claims.

EXAMPLE I Depending upon the other components of the brick batch 5 mix, varying amounts of bentonite will be necessitated in A brick batch mix is prepared from the following: 60 perorder to achieve the benefits of this invention. The amount of cent, by weight, -6 mesh fused alumina grog; 20 percent 48 bentonite utilized will be in the range, by weight, from about 1 mesh sintered alumina fines; percent 325 mesh calcined to 5 percent and preferably from about 2 to 3 percent. It is, of alumina fines; and about 8 to 10 percent 200 mesh silica course, well within the skill of one knowledgeable inthe artto 10 sand. To three separate portions of this mix, there is incordeterrnine the most satisfactory combination of components porated the additives set forth in table 1. Mix A is representawithin the stated ranges for any particular brick batch mix. tive of the prior art and Mix B contains only bentonite. Mix C As stated, the refractory brick batch mix of the present incontains both UP and bentonite in accordance with the vention consists essentially of alumina, silica, a lithium com- 1 5 present invention. Each mix is then tempered with an aqueous pound which will form lithium oxide during burning, and magnesium lignosulfonate solution and hydraulically pressed bentonite. However. small amounts of other materials may be into 9 4lt 2lfi inch bricks at 10,000 p.s.i. Thereafter, the incorporated in the batch mix without deleteriously affecting bricks are fired for 5 hours at 1,450 C. After cooling, the the properties of the resulting brick. For example, phosphoric physical properties and characteristics of the fired specimens acid may be included to enhance the cold strength. Other binare determined by means well known to those skilled in the ders, such as sodium lignosulfonate may be included to impart alt. These results are set forth in table I.

TABLE I Mix A Mix B Mix 0 Additions 0.1% LiF 0.05% 2% bentonite. 2.0 bentonite,

CMOHSg, 0.1% LiF. 0.05% Mg H):- Physical properties:

Bulk density 0z./in. 1.68 1.72 1.72. G./cc 2. 91 2.98 2. 98. Apparent porosity. percent 8.6 18.3 15.7. Modulus of rupture, p.s.i.:

Room temperature 1,800 970 3. 470 1,400" 0 1,160 1,740 1.680 1,5000 s10 1,150 1,380 1,600" 0 660 910 1,350 Deformation under load. 26 p.s.i. at

1,700 O. (1% hrs. hold).

green strength and lubrication. When phosphoric acid is employed, it will usually be present in the range of about i to 4 percent, by weight, preferably from about 2 to 3 percent (as a 75 percent aqueous solution of H3PO4). On the other hand, when a lignosulfonate binder is employed, it will ordinarily be present in an amount of from about i to 2 percent, by weight, as a 50 percent solution in water or from about 0.5 to 1 percent, on a dry basis.

Generally, in preparing bricks from the mixes described herein, the mix will first be tempered with a small amount of water. Some or all of the water may be provided by binders of the type discussed above. In general, the total water will range from about 2.5 to 6 percent, by weight, preferably from about 3 to 5 percent.

In preparing the mix, the materials may be blended in accordance with conventional refractory practice. For example, a muller mixer may be employed in which case it is preferred to first add the coarse materials to the pan along with the major portion of the moisture. This is followed by the finer materials and the remainder of the moisture. Mixing is continued until proper consistency is achieved.

The tempered mix is then pressed into the desired refractory brick shape. It should be noted that the term brick is used in its generally accepted meaning in the refractory art. Specifically, such is not intended to limit in any way the design or physical configuration of the refractories that can be prepared in accordance with this invention. Generally, pressing of the brick necessitates a pressure of at least about 4,000 psi. which may range up to about 15,000 psi. A preferred pressure is in the range of about 8,000 to about 10,000 psi. After pressing and drying, the shaped brick is fired at a temperature which is efiective to provide the ceramic bond. Ordinarily, firing is conducted at a temperature which may range from about 1,200 to l,700 C. and preferably l,300 to l,500 C.

The many facets of this invention are further illustrated by the following examples which are not to be construed as limitations thereof. On the contrary, resort may be had to various other embodiments, modifications and equivalents of As is observable from the results set out in table I, the bricks prepared from Mix C are not only markedly less porous, but they also exhibit superior strength when compared to those from Mixes A and B.

EXAMPLE I] in a manner similar to example I, bricks were prepared from three different mix compositions. Two of the mixes had bentonite and UP incorporated therein. The third (Mix F contained kaolin, Ca(Ol-l) Mg(OH) and LiF but no bentonite. This latter mix was representative of the prior art,

namely, such as was taught by US. Pat. No. 741,333 which was noted heretofore. However, in all of the mixes 3 percent phosphoric acid was used as the binder rather than the Lignin. The specific compositions of each of the brick mixes along with the physical properties of the bricks produced therefrom are set out in table II.

Apparent Porosity, I42 [2.9 .5

Modulus of Rupture,

psi.

Room Temperature .1020 3330 3450 L400 1900 1520 time l.500"( MRO l0 I980 l.600 Ci I720 2090 I080 Deformation Under Load, 25 p.s.i. IV: Hrs. Hold [.700 C. I 0 0 04 it is apparent from the results set out in table II, that while the bricks prepared from Mix F do exhibit desirable physical properties, they are not as good as those from Mixes D and E.

I claim:

cent of said lithium compound and about 2 to 3 percent bentonite.

3. A refractory brick batch mix according to claim 1 wherein said alumina contains at least about 99 percent A50 and said silica contains at least about 99 percent Sit) 4. A refractory brick batch mix according to claim 3 wherein said alumina is at least about 99.5 percent A1 0 and said silica is at least about 99.9 percent SiO,.

5. A refractory brick batch mix according to claim 3 wherein at least about 10 to 35 percent, by weight, of said alumina will be --325 mesh or finer and at least about 50 percent, by weight, of said silica will be -325 mesh or finer.

6. A refractory brick batch mix according to claim 1 wherein said lithium compound is selected from the group consisting of lithium fluoride and lithium carbonate. 7

7. A refractory brick batch mix according to claim 6 1 wherein said lithium compound is lithium fluoride.

8. A refractory brick batch mix according to claim 1 wherein there is incorporated a binder selected from the group consisting of phosphoric acid and sodium lignosulfonate. 

2. A refractory brick batch mix according to claim 1 consisting essentially of, by weight, about 88 to 92 percent alumina, about 5.95 to 9.95 percent silica, about 0.05 to 0.2 percent of said lithium compound and about 2 to 3 percent bentonite.
 3. A refractory brick batch mix according to claim 1 wherein said alumina contains at least about 99 percent Al2O3 and said silica contains at least about 99 percent SiO2.
 4. A refractory brick batch mix according to claim 3 wherein said alumina is at least about 99.5 percent Al2O3 and said silica is at least about 99.9 percent SiO2.
 5. A refractory brick batch mix according to claim 3 wherein at least about 10 to 35 percent, by weight, of said alumina will be -325 mesh or finer and at least about 50 percent, by weight, of said silica will be -325 mesh or finer.
 6. A refractory brick batch mix according to claim 1 wherein said lithium compound is selected from the group consisting of lithium fluoride and lithium carbonate.
 7. A refractory brick batch mix according to claim 6 wherein said lithium compound is lithium fluoride.
 8. A refractory brick batch mix according to claim 1 wherein there is incorporated a binder selected from the group consisting of phosphoric acid and sodium lignosulfonate. 